1. Field of the Invention
The present invention relates to peptidomimetics, capable of inhibiting CD28 and/or CTLA-4 interaction with CD80 (B7-1) and CD86 (B7-2), and pharmaceutical composition-thereof. It also relates to the use of the peptidomimetic for the preparation of pharmaceutical compositions active in pathologies requiring CD28 and/or CTLA-4 agonism or antagonism and method of treating such pathologies.
2. Description of the Background Art
The interaction of antigen Presented in the contex: of MHC class II to the T Cell Antigen Receptor Complex (TCR) provides the primary signal to the Helper T Cell to initiate clonal proliferation. Optimal T cell activation, however, requires a co-stimulatory signal in addition to the engagement of the TCR. Although several co-stimulatory molecules have been implicated in initiating the xe2x80x9csecond signalxe2x80x9d, it has become apparent that one of the major signals is provided by the interaction of CD28 with B7 molecules (CD80 and CD86) presented on the surface of the antigen presenting cell (see FIG. 1).
Cell surface CD28 is a 201 amino acid glycoprotein member of the Ig-superfamily of proteins (Aruffo and Seed., 1987). It is found naturally as a homodimer and expressed constitutively on the surface of 80% of human T cells (all CD4+ cells and on about 50% of the CD8+ cells) and on virtually all murine T cells (Linsley and Ledbetter, 1993) Engagement of CD28 by its natural ligand B7-1 or B7-2 (CD80, CD86) results in a second signal to the T cell and an increase of IL-2 production along with down-regulation of the CD28 with respect to mRNA levels and cell surface expression (Linsley et al., 1993). The second signal is believed to be crucial for the commitment of antigen specific T cell to proliferate. Interference with this second signal in the presence of the first signal (TCR signal) results in antigen specific T cell anergy (unresponsiveness) (Linsley et al., 1992). During the period that CD28 is down-modulated, a closely related glycoprotein, CTLA-4, is concomitantly up-regulated (Freeman et al., 1992). It is generally thought that CD28 delivers the positive costimulatory signal for growth and differentiation, while CTLA-4 is responsible for a subsequent negative signal of the cellular activation events (for a review see Lenschow et al., 1996).
Both CD28 and CTLA-4 bind to the B7 family of proteins, most notably B7-2 and B7-1 (Azuma, et al., 1993). With regard to B7-1, it is known that CTLA-4Ig binds with a 20-100 fold higher affinity than CD28Ig (Linsley et al., 1991).
Freshly isolated human and murine B cells express low levels of B7-2 but not B7-1, however the levels of both 37""s are up-regulated upon activation (Hathcock et al., 1994). In vitro studies have demonstrated that blockade of T cell co-stimulation via the CD28 signaling pathway results in the development of antigen-specific T cell anergy (Harding et al., 1991; Boussiotis et al., 1993; Linsley et al., 1991).
CTLA-4Ig has been used in a wide variety of animal models to study the in vivo efficacy of blocking the CD28 signaling pathway. The first in vivo studies showed that CTLA-4Ig was capable of suppressing humoral responses to a T cell dependent antigen (Linsley et al, 1992).
Other studies have demonstrated that locking the CD28 costimulatory signal is effective in preventing xenograft rejection (Lenschow et al., 1992), cardiac allograft rejection (Turka et al., 1992; Lin et al., 1993), murine systemic lupus (Finck et al, 1994; Chu et al., 1996), graft versus host disease (GVHD) (Wallace et al., 1995), and experimental allergic encephalomyelitis (EAE) (Cross et al., 1995; Perrin et al., 1995; Arima et al., 1996).
Administration of CTLA-4Ig at the time of allogeneic transplantation prolongs the graft survival but fails to prevent rejection (Turka et al., 1992). If one delays the administration of the CTLA-4Ig until 2 days after the transplant, then long-term survival of the allograft is observed as well as tolerance toward subsequent challenge with alloantigen in vivo (Lin et al., 1993; Sayegh et al., 1995).
Judge et al. (1996) recently studied the in vivo mechanism of action of CTLA-4Ig and found that delayed administration of the protein resulted in an 80-90% reduction in Th1-type cytokines and blunted the expansion of antigen specific T cells by 50%. Thus, CTLA-4Ig may be able to regulate the balance between Th1- and Th2-type responses.
In conclusion, there is ample evidence that blockade of the CD28 costimulatory pathway may be a useful therapeutic target for immune modulation. CTLA-4Ig is currently in Phase II clinical trials in psoriasis patients. However its practical use for chronic immunotherapy is limited by it being only parenterally administrable and recurring mg/kg doses.
A small molecule mimetic of CTLA-4/CD28 would have great clinical and commercial advantages and represents a long felt need.
Site-directed mutagenesis studies with both CTLA-4 and CD28 have implicated a hexapeptide stretch including several key sites in the CDR3 region of the protein, MetTyrProProProTyr (SEQ ID NO:31), as a critical contact site in the interaction with B7 (Peach et al., 1994).
European patent application EP 682,039 discloses that CTLA-4Ig fusion proteins block the interaction with B7 antigen. It also discloses CTLA-4 mutants, in which any of the amino acids, including the sequence MetTyrProProProTyr (SEQ ID NO:31), has been replaced by Ala.
International patent application WO 90/33770 is generally Directed to ligands for T cell surface molecules, especially CTLA-4, which induces antigen specific apoptosis of activated T cell. Isolated peptides containing CTLA-4 fragments, constituting the epitope for such binding, are also disclosed and claimed. Such epitopes include the amino sequence ProProTyrTyrLeu (SEQ ID NO:32) (partially overlapping with the above reported hexapeptide MetTyrProProProTyr (SEQ ID NO:31).
Scientists at Glaxo have recently attempted to use both linear as well as conformationally restrained peptides to mimic this region (Ellis et al., 1996). The Glaxo study, however, failed to yield any productive leads.
Citation of any document herein is not intended as an admission that such document is pertinent prior art, or considered material to the patentability of any claim of the present application. Any statement as to content or a date of any document is based on the information available to applicant at the time of filing and does no: constitute an admission as to the correctness of such a statement.
It is an object of the invention to overcome the deficiencies of the related art, such as noted above, by providing biologically active peptidomimetics of CD28 or CTLA-4.
Accordingly, the present invention provides for peptidomimetics of CD28 or CTLA-4 which are capable of inhibiting CD28 and/or CTLA-4 interaction with CD80 (B7-1) and CD86 (B7-2). The peptidomimetics of the present invention contain a core sequence corresponding to amino acid residues 2 to 9 of SEQ ID NO:1 and may be cyclized and may include additional amino acid residues N-terminal and/or C-terminal to this core sequence.
The present invention also provides for a pharmaceutical composition which includes the peptidomimetics according to the present invention, and pharmaceutically acceptable excipients.
Further provided in the present invention is a method of treating pathologies and disorders with are improved by inhibition of CD28 and/or CTLA-4 interaction with CD80 and CD86.